Having absolute pressure control of a hydrocarbon producing well during all drilling and completion operations is an absolute must. This is to protect personnel first and then the drilling rig and other expensive equipment. The main device in place for well pressure control during these operations is the blowout preventer (BOP). BOP's are designed either as ram, ram-shear or annular BOP'S and all are used to seal a wellbore in the event of a blowout. Drilling for hydrocarbons involves penetrating a variety of subsurface geological formations which are layers in the earth. Each layer comprises a specific geologic composition such as, shale, sandstone, limestone, etc. The layers may contain trapped fluids or gas at different formation pressures, and the formation pressures usually increase with increasing depth. The mud weight of the drilling fluid in the wellbore is made heavy enough with barite etc. to overcome the formation pressure. This is done by increasing the density of the drilling fluid in the wellbore or/and increasing pump pressure at the surface of the well.
There are occasions during drilling operations when a wellbore may penetrate a layer having a formation pressure substantially higher that the pressure maintained in the wellbore by the mud weight. When this occurs, the well is said to have taken what is called a kick. The pressure increase associated with the kick is generally produced by gas along with oil, and water or a combination of all of these, and of course the mud is also kicked back with the influx of formation fluids from within the wellbore. The high pressure kick propagates from a point of entry in the wellbore up-hole from a high pressure region below to a low pressure region above. If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling tools may be blown out of the wellbore. These blowouts often result in catastrophic destruction of the drilling equipment including the drilling rig and could cause substantial injury or death to rig personnel.
Because of the of the potential for blowouts, BOP's are either installed at the surface or on the sea floor in deep water drilling arrangements so that kicks may be adequately controlled and circulated out of the system. BOP's may be activated to effectively seal in a wellbore until measures can be taken to control the kick and as stated earlier there are several types of BOP's, the most common of which are annular blowout preventers.
Annular blowout preventers typically comprise annular bulk elastomer donut shaped seals that are forced radially inward to squeeze around the drill pipe and/or running tools to completely seal the wellbore. Another type of blowout preventer is the ram-type blowout preventer. Ram-type preventers comprise a body supporting at least two oppositely positioned cylinders on each side of the through bore with powerful pistons internally which actuate rams. The rams may be pipe rams or variable pipe rams which, when activated, move to engage and surround drill pipe and well tools to seal the wellbore. Shear rams which, when activated, move to engage and physically shear any drill pipe or well tools in the wellbore. The rams are located opposite of each other and, whether pipe rams or shear rams the rams normally against one another at the center of the wellbore. In some cases, ram blocks are used which will effectively shear both rigid and flexible materials that are located in the through bore of the BOP.
Prior art of a couple of pipe ram assemblies are disclosed. A common characteristic of these pipe ram and shear ram blowout preventers is that each individual ram assembly comprises a carrier or holder of some type and a ram block connected to the carrier for limited relative lateral movement. One advantage of the former kind of construction is that each ram assembly comprises a relatively movable carrier and ram block, and a seal may be installed between the carrier and ram block, and such seal may be compressively actuated by relative movement of the carrier and ram block. More specifically, the ram assemblies are moved inwardly.
If the blowout preventer is of the pipe ram type, which simply seals around the outer diameter of the drill pipe, it is fairly convenient to design the structure so that the thicknesses of the ram block and carrier, measured longitudinally with respect to the drill pipe, are generally equal. This is desirable because it maximizes the surface area over which the forces may be distributed.
The present embodiments are detailed below with reference to the listed Figures.